1. Technical Field
The present invention generally relates to vehicle drivelines and more particularly to a differential assembly for a vehicle driveline that selectively transmits power to a set of vehicle wheels.
2. Discussion
Modernly, vehicle manufacturers are employing vehicle drivetrains having more than one drive axle to improve vehicle traction. Common arrangements include part-time four-wheel drive systems that employ a front axle disconnect to selectively disconnect the front wheels from the front of the vehicle drivetrain. These arrangements are commonly known as rear drive/front assist drivetrains. Disconnection of the front wheels from the front of the vehicle drivetrain prevents the front drive wheels from rotating the front of the vehicle drive train at road speed, thereby saving wear and tear on the vehicle driveline. The front axle disconnect also controls the coupling of the front wheels to the front of the vehicle driveline such that the front driveshaft will spin at the same speed as the rear driveshaft.
Despite the relatively widespread use of such drivetrain arrangements, several drawbacks are known to exist, such as their cost and the amount of time that is sometimes necessary for the front axle disconnect to engage and disengage the front of the vehicle driveline to the front wheels. In isolating the front wheels from the rest of the front driveline, front axle disconnects typically use a sliding sleeve to connect or disconnect an axle shaft from the front differential side gear. Vehicle manufacturers typically use either vacuum or heat to move the engagement sleeve and as such, the time that is required to shift the sliding sleeve to a desired position can be relatively long, particularly when heat is employed to heat a fluid to generate sufficient pressure to cause the engagement sleeve to move.
Accordingly, there remains a need in the art for a vehicle driveline that is less costly and which provides improved response in the time for the engagement and disengagement of the vehicle drivetrain to the vehicle wheels.
In one preferred form, the present invention provides a differential assembly having first, second and third structures, a differential gear set and a biasing mechanism. The first structure is configured to rotate along a differential axis in response to receipt of a rotational input. The second structure is supported for rotation on the differential axis. The third structure is supported for rotation on the differential axis and disposed between the first and second structures. The third structure can be operated in an engaged condition for transmitting torque from the first structure to the second structure and a disengaged condition for inhibiting the transmission of torque from the first structure to the second structure. The differential gear set is coupled to and rotatably supported within the second structure. The biasing mechanism biases the third structure in the disengaged condition. The third structure is placed in the engaged condition if a torsional magnitude of the rotational input exceeds by a predetermined amount a torsional magnitude of a rotational force exerted through the differential gear set.
In another preferred form, the present invention provides a vehicle drive train having a transfer case assembly and first and second axle assemblies. The transfer case assembly receives a rotational input from a vehicle power source and produces first and second intermediate rotational outputs therefrom. The first axle assembly is coupled to the transfer case assembly, receives the first intermediate rotational output therefrom and produces a first drive wheel output for rotating a first set of drive wheels. The second axle assembly has a differential assembly with a differential housing member configured to rotate about differential axis in response to receipt of the second intermediate rotational output, a differential case member supported for rotation on the differential axis, a cam member supported for rotation on the differential axis and disposed between the differential housing member and the differential case member and a differential gear set. The cam member can be operated in an engaged condition for transmitting torque from the differential housing member to the differential case member and a disengaged condition for inhibiting the transmission of torque from the differential housing member to the differential case member. The differential gear set is coupled to and rotatably supported within the differential case member. Operation of the cam member in the engaged condition permits the differential gear set to produce a second drive wheel output to rotate a second set of drive wheels. Operation of the cam member in the disengaged condition inhibits the differential from producing the second drive wheel output and permitting the second set of drive wheels to rotate freely.